This invention relates generally to switching apparatus and more particularly to a magnetizing current switch particularly adapted for use with gas insulated power transmission systems.
In recent years, there has come about a demand for a reduced-size substation. This demand on the part of public utilities has been met by gas insulated substation equipment. This type of substation equipment significantly reduces the space required by the high voltage side of substations rated, for example, 46 KV through 500 KV. Space reduction is accomplished by replacing the open-bus and air-tight bushings with gas insulated bus filled, for example, with a highly insulating gas such as sulfur-hexafluoride gas at a pressure, for example, for 45 pounds per square inch gauge, and thereby permitting the movement of electrical equipment very closely together.
This gas insulated substation equipment has many advantages, among which are: significant reduction in space requirements both in land area and overall height; added system reliability by eliminating the possibility of phase-to-phase faults, lightning strokes within the system, or contamination of insulators; reduced maintenance because the closed system is isolated from the environment; added personnel safety because all live parts are covered by grounded shields; and lower installation costs as compared with conventional or other types of power systems when the gas insulated modular approach is utilized.
The gas insulated system, as briefly described above, has additional design strategies, inasmuch as the high voltage equipment is compressed, so that both the space required and the total length of bus is minimized. The power transformers may be located on outside corners so as to be capable of ready removal, and the location of cable parts is flexible, with result that the system may be readily connected to overhead transmission lines.
It is desirable to provide a magnetizing current switch, which will permit the isolation of certain sections of the gas insulating system, and is obvious, quick opening and quick closing of the magnetizing current switch is desirable. Additionally, the magnetizing current switch must be capable of functioning in its installed environment. For example, specifications may require that the magnetizing current switch be capable of a continuous current rating of 2500 amperes, and a switching current rating of 35 amperes.